The present invention relates to the field of power over Ethernet and more particularly to classification of power requirements for high power devices.
The growth of local and wide area networks based on Ethernet technology has been an important driver for cabling offices and homes with structured cabling systems having multiple twisted wire pairs. The ubiquitous local area network, and the equipment which operates thereon, has led to a situation where there is often a need to attach a network operated device for which power is to be advantageously supplied by the network over the network wiring. Supplying power over the network wiring has many advantages including, but not limited to: reduced cost of installation; centralized power and power back-up; and centralized security and management. In the Ethernet technology field, supplying power over an Ethernet interface is referred to as Power over Ethernet (PoE).
Several patents have addressed this issue, including: U.S. Pat. No. 6,473,608 issued to Lehr et al., whose contents are incorporated herein by reference and U.S. Pat. No. 6,643,566 issued to Lehr et al., whose contents are incorporated herein by reference. Furthermore a standard addressed to the issue of powering remote devices over an Ethernet-based network has been published as IEEE 802.3af 2003, whose contents are incorporated herein by reference, and is referred to hereinafter as the “af” standard. A device receiving power over the network wiring is referred to as a powered device (PD) and the powering equipment delivering power into the network wiring for use by the PD is referred to as a power sourcing equipment (PSE).
The “af” standard limits the amount of power available to a powered device to 12.95 watts, and devices demanding power in excess of the 12.95 watt power limit are not supported. In order to meet growing power demands, in particular demands for PDs drawing in excess of 12.95 watts, a task force entitled “IEEE 802.3at DTE Power Enhancements Task Force” was formed, which produced a higher power standard, hereinafter the “at” standard. The “at” standard specified a higher current limit than the “af” standard, and PSEs meeting the “at” standard are required to support PDs meeting the “af” standard. Devices according to the “af” standard are hereinafter alternatively denoted low power devices and devices according to the proposed “at” standard are hereinafter alternatively denoted high power devices. It is to be noted that high power devices may draw less power than an “af” device, however operation is according to the proposed “at” standard for high power devices.
The “at” standard exhibits certain interoperability conditions regarding “af” and “at” equipment. For example, in the event that an “at” PD is connected to an “af” PSE, it is an objective that the “at” PD will notify the user that the power sourcing equipment is of the “af” variety, and thus unable to support full powering under the “at” standards. Similarly, an “at” PSE having an “af” PD attached thereto is expected to identify the PD as being an “af” PD, and further support powering in accordance with the “af” standard. Preferably, such mutual identification is unambiguous, and operates consistently.
In order to improve overall system power and load management, the “af” standard provides for PD classification to one of four potential classes. Each class exhibits a range of maximum power drawn by the PD. Unfortunately, of the four potential classes, class 4 is reserved for future use, and class 0 is defined as a default class in which no power requirement information is supplied by the PD. Thus, effectively only three power requirement classes are provided. The “at” standard is expected to provide additional classes; however, as indicated previously, any classification method must provide for cross compatibility and avoid ambiguity.